Abstract: The locating problems of endwise insertion of baffles into tubular heat exchanger headers and/or weakness problems resulting from slotting tubular heat exchanger headers for receipt of baffles are avoided in a heat exchanger including opposed headers 10, 12, at least one of which is a header tube 12 having a plurality of slots 26, 30 in a side thereof. A plurality of generally parallel tubes 14 extend between the headers 10, 12 and enter an associated one of the slots 26, 30, while a baffle is located in the header tube 12 and divides the same into two discrete sections and includes a collar 40 about an end 28 of one of the parallel tubes 14.